'I used to feel intimidated.Not any more'

Her book Eats, Shoots and Leaves has now notched up two million sales. Here Lynne Truss explains why a lifetime of low self-esteem and the death of her sister are the real story behind its phenomenal success

She has licked Harry Potter to a custard. She is America's number-one bestseller from New York to San Francisco. Despite her book's fearsome subtitle ('The Zero Tolerance Approach to Punctuation'), she is outselling hot-cakes in Korea, Hong Kong, Singapore and Australia. And, in the age of Bush and the war on terror, her quirky little guide to commas and semi-colons has become a global hit.

The nice thing about Lynne Truss is that she still can't quite believe it. 'It's really surreal,' she says, with the puzzled expression of a shy forest creature. 'You do think that someone is having a laugh here, and I've been set up.'

Well, she has been set up, of course. For life. So now she finds herself doing sums all the time, cautiously halving the estimate of her new riches 'because all sorts of people are going to take cuts'. Quite apart from the scale of the thing, it has all happened so fast. 'I do a lot of very strange calculations which a year ago I wouldn't have believed I would be doing.'

When lightning strikes in the world of books, its victims can be scorched beyond recognition. Lynne Truss, however, meets her good fortune with the wisdom of experience, with characteristic English phlegm, and with an instinctive irony. When she was asked on American television if she intends to make a film of Eats, Shoots and Leaves, she replied, deadpan: 'Julia Roberts as an apostrophe and Schwarzenegger as an exclamation mark.'

The jokes come naturally. She has a detached and humorous view of life and has always wanted to be a comic writer. As a child of the mid-Fifties, she read Molesworth and AP Herbert and listened to Tony Hancock records with her parents, whose taste was more Steptoe than the Goons. The title of her book comes from the gag about the panda which has been a staple for British comedians since the Fifties, and probably before.

I suspect that Truss's sense of humour conceals a fairly well-defended inner melancholy. Behind the laughter and the overnight success - which is nothing of the sort; Truss has been writing for years - is a sadder story of a woman lacking in confidence who has had to conquer a number of real and imagined obstacles to become the writer she is today.

She was a late starter. 'I didn't begin writing properly until I was in my mid-thirties,' she says. 'I had to overcome a big barrier. I thought that people were born with the right sort of certificate that said, "This person is allowed to write" and I didn't have it.' Truss underwent therapy to tackle her self-esteem problems and to liberate her urge to write. She now says it was 'class' that prevented her from feeling 'good enough to write'.

Truss grew up on a working-class council estate near Richmond, west London. Her father was a self-taught accountant who did the books for the company which made Sellotape. Her mother was a former telephonist. Neither sounds ambitious for themselves or their daughter, but she was hardly deprived.

Hers was a classic suburban upbringing - a tight-lipped, stable, reasonably secure, not-very-joyful double-income family in which young Lynne would sit on the stairs, retreat into the adventures of Rider Haggard and John Wyndham, and keep herself apart.

'It was a very divided family,' she says. 'No one was happy.' Her parents were not bookish, but, she says: 'They were both interested in writing. I think there was always an idea that to write a book was probably the biggest achievement you could have.'

When she describes her upbringing, she sounds like an only child, but it turns out that she had an older sister with whom she was close in a complicated and competitive way. She says of her family that 'there were always feuds going on, and people not speaking to each other', but thanks to the 1944 Education Act, she was able to escape. She passed her 11 plus, went to Kingston Grammar, and then on to London University, where she was lucky enough to be taught by John Sutherland and AS Byatt.

Her first job was working as a sub-editor on the Radio Times. Then she went to the Times Higher Educational Supplement, from there to the Listener, where she became literary editor and also wrote a column. The Listener, alas, is long gone and her column long lost. But it survives, in a pureed form, in a book she published in 1995, Making the Cat Laugh, in which she strung together her observations of 'single life on the margins' into a wry and comic account of Being Lynne Truss.

That was rather ahead of its author's time, but now that she's a global mega-hit, her publisher is reissuing this volume, together with three comic novels (Going Loco, Tennyson's Gift and With One Lousy Free Packet of Seeds). These four volumes will certainly gratify anyone who has actually read Eats, Shoots and Leaves, and further demonstrate a sprightly, self-deprecating humour and intermittently betray that continuing battle with her self-esteem. Going Loco begins: 'Since being the heroine of her own life was never quite to be Belinda's fate...' When it came out in 1999, that was probably quite an accurate summary of Truss's situation.

Eats, Shoots and Leaves has certainly made her the heroine of her own life and put a spring in her step. 'I feel more centred in my life, to be honest,' she says. 'With the book [ Eats, Shoots and Leaves ], there's one amazing change, which is that I've always been very intimidated by the world and at the moment I'm not. I'm not as worried about people's opinions as I was. I mean I still hurt, but I just feel, "Well, I don't care, it's their problem."'

Sadly, for those who might want to attribute this transformation to good reviews, this new toughness comes not from massive sales but from great per sonal pain: 'My sister died three-and-a- half years ago and that was the biggest family event in my life.' Truss says that her sister's death has made her re-evaluate herself. She has also had to come to terms with the nature of that relationship. 'One of the awful, tragic things about her dying is that she would have hated this [success]. She would have been very unhappy about [the book] doing so well, because she always hated it when nice things happened.'

The genesis of Eats, Shoots and Leaves has been widely described (popular Radio 4 programme... publisher's book-party commission... written to a rushed deadline... unexpected rave reviews), but Truss now comes close to conceding that she could not have done this while her sister was alive. 'I just feel that, somehow, I'm allowed to have this now,' she says. And when she goes on, that old self-esteem problem recurs, 'I obviously didn't deserve it before, but I feel as though it somehow couldn't have happened. I would have been just too worried about how it would have affected my sister.'

On the table between us as we speak is a huge pile of Eats, Shoots and Leaves, all signed by the author, but just at this moment all that feels pretty unimportant.

'I think going through the death of someone you love, and surviving it... when you feel as though you've terribly let them down because they died and you didn't, I think all that gets you into perspective.'

Does this change her view of life? 'Well, you do think: "Enjoy things while they're good." At the moment in my life, nobody's dying. As you get older the periods between grief get shorter, and you just sort of enjoy the bits when there's nothing horrible happening. It's not a great philosophy, and not very profound, but it's what I've arrived at.'

If Truss has an inkling about what's important to her now, she is agreeably puzzled by the success of her little book. 'With everything that's going on in the world, it is rather odd that people should be concerning themselves with semi-colons. There must be a real comfort in looking at something with sets of rules, and which you can also have fun with when there are so many awful things going on. Some people buy it for instruction because a lot of people haven't been taught much about grammar. There are a lot of very bright people around who have never had the training and who wonder, "Why do I put the apostrophe in?"'

Despite this air of puzzlement, she was never terribly surprised. (After all, at two million copies and rising, you'd have to feel pretty confident that you were doing something right.)

'I did have this moment of clarity. I was here [at the publishers] signing copies before publication, and there was a flap about a reprint, and they were saying, "We could do 10 or 15 thousand." And I said, "I don't think you'll be stuck with them."'

None of this certainty saved her from the usual visitation of worries. Lynne Truss is the kind of person who gains peace of mind by making lists of things to do. Last Christmas, when the book was the season's sensation she found herself worrying about Uncle Fred. 'I signed a lot of copies for Uncle Fred. It was, "Oh, Uncle Fred, he's such a stickler!" and I thought there was a danger that Uncle Fred would get 10 copies for Christmas and he'd take nine of them back on Boxing Day, and we'd have the biggest churn rate of any book in history.'

Fortunately, it turned out that dear old Uncle Fred simply loved having 10 copies. It became a matter of pride with dyed-in-the-wool sticklers and pedants to note how many copies they got for Christmas. Ian Hislop, apparently, got no fewer than five.

The delight Lynne Truss has brought to the nation's sticklers and the honest satisfaction she will no doubt soon be giving her bank manager when the accountants have done their worst, has not been an unmixed blessing to Truss herself. Eats, Shoots and Leaves has 'transformed my life' she says. 'I hardly write a thing now. I talk much more than I write at the moment, and that's very strange.'

Now, fresh from the rigours of the American book promotion circuit, she longs to retreat to her flat in Brighton and get stuck into her next project, a set of radio monologues (she describes herself as a writer and broadcaster). In 2002, before she was famous, she did a sequence about women in their forties, and now wants to do a similar set about men - 'Stories about a father, a brother, a son...'

'I like writing men,' she says, and, although she has never married, adds with slight defensiveness: 'I've lived with lots of people... about half my adult life. It's much more that I've been with people than without really. But when I'm without people, I tend to write about it, because I feel so happy.' She glosses this quickly. 'But I don't hate men or anything. I really like men.' She adds that when she's asked to comment by her women friends on a relationship break-up: 'I often see the man's point of view'.

She does not encourage further exploration of this subject, but her books certainly suggest a woman who has, for one reason or another, not stumbled across the right partner. Perhaps nice, funny, accommodating Lynne Truss has been too eager to please. 'If I was to get analytical about it, to make my dad laugh was probably what I've been trying to do all my life.'

She's fairly sure than even if he didn't laugh at Eats, Shoots and Leaves, her father would be proud of her success. And that's enough to be going on with in the Man Department. She gets quite annoyed by newspaper critics who say that her interest in punctuation means that, by definition, she doesn't have a life. She smiles at the irony that's coming into view.

'Of course I have no answer to this because doing the book did deprive me of a life. So when people say, "You ought to get a life", I reply, "You're right. Absolutely. There's just no time to get one."'

For the moment, she seems happy enough at the prospect of her well-crafted, domestic English comedies getting a new lease of life in the bookshops. 'I think making people laugh is a great joy,' she says, simply.